Former-press section in a paper machine and method for transfer of the web from the former to the press section

ABSTRACT

The invention relates to a former-press section ( 100, 110 ) of a paper machine and to a method of transferring a web from a former to a press section. Between the former section ( 100 ) and the press section ( 110 ) there is a pre-press zone (PP) which removes water from the web (W) and through which the web (W) is passed as a closed draw from the former section ( 100 ) to the press section ( 110 ). The upper wet wire ( 10 ) or the equivalent transfer wire ( 10 A) of the former section ( 100 ) is passed through the pre-press zone (PP), the web (W) being passed on the lower face of said wire into and through the pre-press zone (PP). Inside the loop of the upper wet wire ( 10 ) or of the equivalent transfer wire ( 10 A) and/or inside the loop of the lower wet wire ( 20 ) there are transfer devices ( 15, 15   a   , 16, 26 ) based on the use of a pressure difference. The transfer devices ( 15, 15   a   , 16, 26 ) are arranged to operate in connection with threading or an operational malfunction such that the web (W) is separated from the upper wet wire ( 10 ) or the equivalent transfer wire.

FIELD OF THE INVENTION

The invention relates to a former-press section of a paper machine inwhich the former section comprises a lower wet wire and an upper wetwire or an equivalent transfer wire, and in which the press sectioncomprises one or more dewatering press nips, and between which formersection and press section there is a pre-press zone which removes waterfrom a web and through which the web is passed as a closed draw from theformer section to the press section.

The invention also relates to a method of transferring a paper web froma former section of a paper machine to a press section thereof, whichformer section is provided with a lower wet wire and with an upper wetwire or with an equivalent transfer wire, and which press section isprovided with one or more dewatering press nips, and between whichformer section and press section water is removed from the web in apre-press zone through which the web is passed as a closed draw from theformer section to the press section.

BACKGROUND OF THE INVENTION

Increased speeds of paper and board machines provide new problems to besolved, which problems are mostly related to the rumnnability of themachine. Currently, speeds of up to from about 1600 to about 1700 metersper minute are employed in paper machines. At these speeds, theso-called closed press sections, which comprise a compact combination ofpress rolls fitted around a smooth-faced centre roll for the most partstill operate satisfactorily. The applicant's Sym-Press II™ andSym-Press O™ press sections may be mentioned as examples of these presssections.

Dewatering taking place by pressing is more advantageous than dewateringby evaporation from the point of view of energy economy. For thisreason, attempts should be made to remove a maximal amount of water fromthe web by pressing, in order that the proportion of water to be removedby evaporation could be made as low as possible. Increased speeds ofpaper and board machines, however, provide new, so far unsolved problemsexpressly for dewatering taking place by pressing because the pressimpulse cannot be increased sufficiently by the prior art means, aboveall because at high speeds the nip times remain insufficiently shortand, on the other hand, the peak pressure of compression cannot beincreased beyond a certain limit without destroying the structure of theweb. In addition to the drawbacks mentioned above, the efficiency of theprior art suction rolls is lowered significantly at particularly highweb speeds, because the suction does not have sufficient time to actupon the web in the intended manner through the relatively longperforations in the mantle of the suction roll and through non-porousand thick pick-up press felt. This both limits the efficiency ofdewatering and makes the transfer of the web more difficult with thehelp of a vacuum in the suction roll.

With increasing speeds of paper machines, the problems of runnability ofa paper machine are also manifested with higher emphasis, because a webwith a high water content and low strength does not endure especiallythe dynamic forces produced by high web speeds and changes in thedirection of the web, but rather web breaks and other operationalmalfunctions arise, causing downtime periods. In modern printing papermachines, the cost of downtime is today about FIM 50,000 per hour.

In the prior art press sections, the web is generally passed from theforming wire into the first press nip on a pick-up felt, which alsooperates as a press fabric that receives water in the first press nip,which is either a roll nip or an extended nip. In the first press nip, arelatively high compression pressure is employed and large quantities ofwater are dealt with, and it is one of the drawbacks arising from thisthat the outer face of the press felt tends to be contaminated and itsporous fabric structure tends to be partially blocked. Attempts are madeto prevent this by means of efficient felt conditioning devices, whichare, however, quite expensive, spacious components which consume anabundance of energy.

Recently, even speeds as high as about 40 meters per second=2400 metersper minute have been contemplated as speeds of printing-paper machines.Applications at speeds as high as this, in particular in wide machines,provide ever more difficult problems to be solved, of which problems themost important ones are runnability and adequate dewatering capacity ofthe machine at a high web speed. Similarly, in board machines (basisweight of the web>100 grams per square meter) attempts are made toincrease the present web speeds (8-15 meters per second) to the level of15-25 meters per second.

Important drawbacks of the press felts used in the prior art presssections include the effect of rewetting the web and the tendency ofcontamination, because, in particular when said press felts run througha high-pressure nip or nips, particles of contaminants tend to beaffixed and to adhere to the press fabrics, wherefore the operation ofthe press fabrics is disturbed and their cleaning requires efficientconditioning devices, which consume a considerable amount of energy.

Moreover, in high-pressure press nips, the prior art porous press feltsare subjected to intensive wear and strain, so that the felts must bereplaced rather frequently, which increases the costs to a considerableextent.

With respect to the prior art related the invention, reference is madeto U.S. Pat. Nos. 4,197,158, 4,879,001, 5,308,450 and 5,736,011. Thelast-mentioned U.S. Pat. No. 5,736,011 discloses a wet end of a papermachine which comprises a headbox of special construction and atwin-wire former on whose upper wire a web is passed as a closed draw toa pick-up point. The US patent does not disclose a pre-press nip nor anypre-pressing stage integral to the present invention. A furtherdifference is that the present invention does not have the speciallimitations and structural requirements described in the above-mentionedUS patent in connection with the headbox. The geometry of the twin-wireformer and the transfer of the web from the former to a press sectiondisclosed in the US patent are also substantially different from thoseof the present invention.

With respect to the prior art most closely related to the invention,reference is made to the applicant's FI patent 98843 (corresponding WO97/13030 and U.S. Pat. No. 5,792,320). This FI patent discloses a methodfor removing water from a paper or board web and for passing it as aclosed draw from a forming wire or transfer wire of a web former sectionto a press section. In the method of the FI patent, the web running onthe forming wire or on the transfer wire is caused to adhere in atransfer and pre-press zone to the outer face of a transfer belt whichis substantially non-water-receiving, and after the pre-press zone, theweb is separated substantially immediately from said wire and passed onsupport of the transfer belt loop onto the next press fabric and/or intothe next press nip in the press section.

In addition, the above-mentioned FH patent discloses a press section inwhich the press section includes a pre-press zone or zones and atransfer belt loop which is substantially non-water-receiving and has anouter face capable of adhesion to the paper web. This transfer belt loopis passed through the pre-press zone, or if two zones are present, atleast through the latter zone. In the pre-press zone, the paper web iscaused to adhere to the outer face of the transfer belt loop, and afterthe zone, it is separated substantially immediately from the formingwire without substantial rewetting of the web. On the transfer belt, theweb is passed as a closed and supported draw onto the next press fabricand/or through the next press zone in the press section.

In FI patent 98843, a reliable and closed draw of the web isaccomplished from the former section to the dryer section without riskof rewetting of the web. Also, in connection with the forming wire or anequivalent transfer wire it is possible to arrange one or more pre-presszones in which the web is caused to adhere reliably to the transfer beltwhich is substantially non-water-receiving, and moreover, a substantialamount of water is removed, which increases both the dry solids contentand the wet strength of the web. This again improves the runnability ofthe press section and facilitates later stages of dewatering.

Drawbacks of the method and the press section disclosed in theabove-mentioned FI patent 98843 include at especially high web speeds inparticular difficulties in passing the paper web and the edge strips cuttherefrom into a pulper in connection with threading or a disturbance inoperation, since in the FI patent, the upper fabric tends to carry theweb with it, although the pre-press nip would be even open. This causesweb breaks and other operational malfunctions in the press section.

With increasing speeds of paper machines, the above-noted web transfer,pick-up and dewatering capacity problems and other difficultiesassociated with them are aggravated.

An object of the present invention is to develop further the method fortransferring and pressing a paper web and the press section disclosed inthe above-mentioned FI patent 98843 so that the advantages attainable bythe FI patent are also retained in the present invention.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is to provide a new combination of aformer and a press section of a paper machine as well as a method in thetransfer of a web from the former section to the press section so thatthe above-noted drawbacks are mainly avoided and the other objects ofthe invention explained later are achieved.

With a view to achieving the objects stated above and those which willcome out later, the former-press section in accordance with theinvention is mainly characterized in that said upper wet wire or anequivalent transfer wire of the former section is passed through saidpre-press zone, the web being passed on the lower face of said wire intoand through said pre-press zone, that inside the loop of said upper wetwire or of said equivalent transfer wire and/or inside the loop of alower wet wire there are transfer devices based on the use of a pressuredifference, by means of which transfer devices it is ensured in a normalsituation of operation that the web is separated from the lower wet wireand follows the upper wet wire or the equivalent transfer wire and runson the lower face of said wire further into the pre-press zone, and thatsaid transfer devices based on the use of a pressure difference can bearranged to operate in connection with threading or an operationalmalfunction such that the web is separated from the upper wet wire orthe equivalent transfer wire and falls down into a wire pit, pulper orequivalent situated underneath.

The method in accordance with the invention is in turn mainlycharacterized in that, after forming of the web or at its final stage, apressure difference is applied to the web through said wet wires andthrough a transfer wire, if any, by means of particular pressuredifference devices such that the pressure acting on the web is arrangedin said pressure difference devices to be higher on the side of an upperwet wire or an equivalent transfer wire with the result that, inconnection with threading or an operational malfunction, the web ispassed to follow a lower wet wire, and said pressure is arranged to behigher on the side of the lower wet wire with the result that, in anormal situation of operation, the web is passed to follow the upper wetwire or an equivalent transfer wire.

By means of the method and the device of the invention the web is madeto reliably follow the upper wet wire or an equivalent transfer wire ina normal situation of operation directly into a pre-press zone or,alternatively, in case of a disturbance in operation or in connectionwith threading, the web is made to reliably follow the lower wet wirebefore the pre-press zone so that the web and its edge strips do notcause disturbance in the pre-press zone and in the press zones properfollowing after it. The devices based on a difference in pressure inaccordance with the invention enable said transfer to be efficientlyensured because the permeability of the wet wire or wires and thetransfer wire, if any, is relatively high and thus, through it, theeffect of a pressure difference can efficiently be applied to the webwithout excessive energy consumption or other disturbing factors. In thepre-press zone applied in the invention, because of the above-mentionedhigh permeability of the wires, considerable amounts of water can beremoved using a moderate amount of energy so that the web can be passedeven at high speed in a reliable manner to the press section proper andthrough it and further to a dryer section. Moreover, the formation ofthe web and its z-direction distributions can still be affectedefficiently in the pre-press zone.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in detail withreference to some exemplifying embodiments of the invention shown in thefigures of the accompanying drawing, to the details of which embodimentsthe invention is not by any means narrowly confined.

FIG. 1 is a schematic side view of a first embodiment example of theinvention.

FIG. 2 shows, in a manner corresponding to that of FIG. 1, an embodimentof the invention in which a paper web is passed from a pre-press nip ofan upper wet wire as a closed draw through the entire press section on alower impermeable transfer belt.

FIG. 3 shows, in a manner corresponding to that of FIGS. 1 and 2, anembodiment of the invention in which a pre-press nip in a press sectionis followed by two successive two-fabric extended-nip presses.

DETAILED DESCRIPTION OF THE INVENTION

The general arrangement and the common structural features of the formerand the press section shown in FIGS. 1, 2 and 3 are described below.

The paper machine schematically shown in FIGS. 1, 2 and 3 comprises aformer section 100, a press section 110 and a dryer section 120, onlythe initial end being shown of the last-mentioned section.

The former section 100 shown in FIGS. 1-3 is a twin-wire formercomprising an upper wet wire 10 and a lower wet wire 20. The wires 10,20 define between them a twin-wire zone which begins from a forming gapG, into which a pulp suspension jet is supplied from a discharge openingof a headbox 19. After the forming gap G, the twin-wire zone curves in asmall curve sector over a suction zone or zones 21a of a first formingroll 21 situated inside the loop of the wire 20. In the twin-wire zonethere are after that forming members 12, for instance, a so-called MBunit, placed inside the loop of the upper wire 10, which MB unitcomprises successive rib elements known per se and loadable against oneanother by loading hoses.

The upper wet wire 10 is guided by a breast roll 11 and guide rolls 13.The forming members 12 are followed by a forming shoe 22 situated insidethe loop of the lower wet wire 20, which forming shoe has a curvedribbed deck, and after that there is a second upper forming suction roll24 on whose suction zone 24 a the twin-wire zone curves changing fromvertical to horizontal.

As shown in FIGS. 1-3, in the horizontal run of the twin-wire zone thereare suction devices 25 and 26 inside the loop of the lower wet wire 20,and between them there is a suction device 15 inside the loop of theupper wet wire 10. The suction device is shown to be a suction rollhaving a suction zone 15 a. After the suction device inside the wet wire10 there are three successive suction flatboxes 16, before which a web Whas already been separated from the lower wire 20, when the web W ispassed from the former section 100 to the press section 110 in thenormal manner. The suction flatbox 26 situated inside the lower wireloop 20 after the suction device 15 is followed by a guide roll 23 awhich guides the lower wire 20 apart from the web W and from the upperwire 10. The lower wire 20 is otherwise guided by its guide rolls 23 onits return run.

Although in the embodiment of the invention illustrated in FIGS. 1, 2and 3 the former is expressly a twin-wire former, it shall be understoodthat the method of the invention and the combination of the formersection and the press section may also be applied when the former is,for example, a hybrid former having a single-wire initial portion or amulti-layer former or even a Fourdrinier former which is provided withan upper wet and/or transfer wire, which corresponds to the above-notedupper wet wire 10 while the lower wire is a normal Fourdrinier wire 20.With respect to the different former concepts in connection with whichthe invention may be applied, reference is made, as some non-limitingexamples, to the formers described in the applicant's above-mentioned FIpatent 98843.

In FIG. 1, the largest horizontal machine-direction extension of theformer section 100 is designated by H₀, the corresponding horizontalextension of the twin-wire zone is designated by H₁, and thecorresponding extension of the upper wet wire loop 10 from the end ofthe twin-wire zone to the outermost guide roll 13 a is designated by H₂.It is typical of the geometry of the former, specifically a twin-wireformer, in accordance with the invention that the horizontal extensionof the upper wet wire loop 10 after the twin-wire zone is relativelylarge, and preferably H₂ >H₁ or H₂ ≈H₁ and generally H₂ ≈(2−4)×H₀.

In accordance with the invention, the upper wet wire 10 takes the web Won its lower face to a pre-press nip PP. The pre-press nip PP is formedbetween a press roll 17, which is situated within the upper wire loop 10and provided with a recessed face 18 (a smooth-faced roll is alsopossible), and a lower shoe roll 42 provided with a flexible hosemantle. Thus, the pre-press nip PP is an extended nip whose compressionload is produced by hydraulically loading a press shoe 43 inside themantle of the shoe roll 42 against the back-up roll 17.

As FIGS. 1-3 show, the web is separated after the pre-press nip PPsubstantially immediately from the upper wet wire 30 in order to preventrewetting by attaching the web W to the smooth and adhesive outer faceof a lower transfer belt 40A,40B, on which the web is transferredwithout substantial rewetting because the transfer belt 40A;40B is notsubstantially water-receiving.

The press section shown in FIGS. 1 and 2 includes as the press nipproper one press nip N₁, which is formed between an upper press roll 32provided with a recessed face or with a smooth face 33 and a lower shoeroll 62 provided with a flexible hose mantle. The loading of theextended-nip zone in the nip N₁ is produced by means of a hydraulicpress shoe 63 situated inside the hose mantle of the shoe roll 62.

In FIG. 3 there is, in addition to the extended-nip zone 61 describedabove, a second extended-nip zone N₂, which is formed by a lower pressroll 82 provided with a smooth mantle face 83 and by an upper shoe roll52 provided with a flexible hose mantle and having a press shoe 53 atthe extended-nip zone N₂.

One characteristic feature of the paper machine shown in FIGS. 1—3 isthat the paper web W has a very linear run from the beginning of thetwin-wire zone and even from the second forming roll 24 up to a dryingwire 90 so that the largest angle of the change of direction of the webW on this run is of the order of 10-20°, said angle of the change ofdirection being preferably smaller than about 15°. Partly owing to thisfeature, the web W will have a trouble-free and reliable transfer evenat very high web speeds

In connection with the beginning of threading or when there has occurreda disturbance in operation, the web W can be passed from the former 100down into a wire pit (not shown) or into an equivalent pulper before theweb W is transferred into the pre-press nip PP and to the press section110. When the web W is desired to be passed down into a wire pit or intoa pulper, the travel of the web W on the face of the lower wet wire 20is ensured by means of vacuums in the suction devices 26 situated insidethe loop of the lower wet wire 20 and, at the same time, the travel ofthe web W with the upper wet wire 10 is prevented by closing the vacuumzone 15 a of the transfer suction device 15 or even by means of apositive pressure introduced into it 15 a. When the web W is desired tobe passed into the pre-press nip PP and, at the same time, further intothe press nips proper N₁;N₁,N₂ of the press section 110, a vacuum isquickly connected to the suction zone 15 a of the transfer suctiondevice 15 and simultaneously, when needed, the vacuum level in thesuction device 26 can be additionally lowered. The web W will thenfollow the upper wet wire 10 up to the pre-press nip PP. The pick-upprocedure described above can also be performed by a lowering movementof the transfer suction device 15, which is illustrated by the arrowU-D. The lowering and raising movement (U-D) of the transfer suctiondevice 15 is produced in both edge areas of said device by means ofpower devices, such as hydraulic cylinders or equivalent fitted, forinstance, in connection with both bearing supports of the transfersuction roll 15.

Since the permeabilities of the wet wires 10,20 or of the correspondingtransfer wire 10A and the lower wet wire 20 are inherently fairly high,an efficient pressure difference effect can be applied through them forguiding the travel of the web W so as to follow either the upper wetwire 10 or the equivalent transfer wire 10A or the lower wet wire 20according to the requirements of the operating situation at any giventime. In addition, dewatering through the upper wet wire 10 or theequivalent transfer wire 10A in the pre-press zone PP is efficient forthe same reasons. The air permeabilities of the wires 10,20;10A,20 aretypically in the range of from 3000 to 8000 m³/m²/h when the pressuredifference is 100 Pa.

The lower fabric running through the pre-press nip PP is a transfer belt40A,40B which is substantially impermeable to water and which has such arunning path that the web W passed on its face from the pre-press nip PPcan be separated, in case of a break or in connection with starting ofthe machine or in connection with threading of the web W, by means of adoctor 44 from the transfer belt 40A,40B and passed down into a pulper(not shown) or equivalent. This means in practice that, in the pre-pressnip PP, the wet wire 10 is substantially in an upper position and thetransfer belt 40A,40B is substantially in a lower position.

Although in the foregoing and in the following reference is made to theupper wet wire 10 and to the lower wet wire 20, the concept of theformer section 100 may also differ in this respect from those shown inthe figures, and the run of the upper wire loop 10 taking the web W fromthe twin-wire zone into the pre-press nip PP need not be horizontal,but, instead, it may alternatively be either obliquely upwards orobliquely downwards.

In the twin-wire zone before the transfer device 15 there are watercutting means 14 from which water jets S are directed through the wire10 for cutting edge strips from both edges of the web W so as to producea flawless web W of uniform width whose width is precisely determined.The cutting width of the web W can be arranged to be adjustable byadjusting the location of the water cutting means 14 in a transversedirection in a manner and by devices known in themselves. The watercutting of the edges of the web W and the adjustable suction width ofthe transfer suction device 15 enable a web W with good edges to bepassed into the pre-press nip PP and into the press nips proper. Theedge strips of the web W are passed with the lower wet wire 20 into awire pit (not shown).

In accordance with the method of the invention, when the web W isbetween the two wires 10,20, it is transferred onto the lower face ofthe upper wire 10 and on it forwards. The beginning of the transfer ofthe web W can be accomplished such that, when the web W follows thelower wire 20, the upper wire 10 and the suction roll 15 are broughtinto contact with the lower wire 20 and the web W is then transferredonwards together with the upper wire 10. When the web W is desired to bepassed into a pulper, the suction roll 15 on the side of the upper wire10 can also be lifted up (arrow U-D). The transfer may also be carriedout the other way round: when the web W follows the upper wire 10, theweb W is guided into the pulper by raising the lower wire 20 and asuction roll (not shown) placed inside it into contact with the web W.The preferable transfer alternative is the latter one in which the web Wnormally follows the upper wire 10. In that case, the web W can bepassed directly after forming into the pre-press nip PP, and the web Wneed not be transferred in the wire section from one fabric ontoanother.

FIGS. 1, 2 and 3 depict the pre-press nip PP expressly as an extendednip which is formed between the shoe roll 42 and the upper press roll17. The press roll 17 preferably has a recessed face 18 or the roll 17is a suction roll and, when needed, an adjustable-crown roll. The lowershoe roll 42 in the pre-press nip PP has a hose mantle 42′ provided witha smooth outer face. Although the pre-pressing PP is preferably carriedout by an extended-nip press, a roll nip is also possible as thepre-press PP. The pressing stages proper are also preferably carried outby means of extended-nips N₁;N₁,N₂, but, alternatively, a roll nip orroll nips are possible.

The object of pre-pressing PP is to raise the dry solids content of theweb W before the web W is transferred into the press nips properN₁;N₁,N₂ but, since pressing is started in the pre-press nip PP at afairly low dry solids content k₀≈10-15%, the formation of the web W mayalso be improved by mean of pre-pressing. In the pre-press nip PP, theformation of the web W may be affected by working the fibre mesh of theweb at the stage where the web W is already relatively frozen. Thestructure of the web W can then be worked by means of the relativelyhigh compression pressures used in the pre-press nip PP, and shearingstresses can be produced in the web W by means of pressure. with theresult that fibre flocs will disintegrate and become loose, and it ispossible for the fines to be displaced in the web, which has afavourable effect on the z-direction distributions in the structure ofthe web W.

A substantial amount of dewatering also takes place in the pre-press nipPP so that the dry solids content of the web can be raised from theabove-mentioned value k₀ to the value k₁≈18-35%.

The transfer of the paper web W from the former 100 up to the dryersection 120 preferably takes place as a closed draw.

The structural features differing from one another in different FIGS. 1,2, and 3 are described in the following.

In FIG. 1, the web W is transferred from the pre-press nip PP on theface of the lower transfer belt 40A, and from it by means of a vacuum ina suction zone 31 a of a transfer suction roll 31 onto the face of theupper felt 30 and further into the press nip N₁. One of the pressfabrics in the nip N₁ is a lower transfer belt 60, on whose upper facethe web W is transferred from the nip N₁ to a point where the web W istransferred by means of a vacuum in a suction zone 91 a of a transfersuction roll 91 onto a drying wire 90 and on it to cylinder drying 92 orequivalent. In FIG. 1, the first guide roll of the lower transfer belt40A is denoted with the reference 41 a and the last guide roll thereofwith the reference 41 b, in a corresponding way, the first guide roll ofthe second transfer belt 60 is denoted with the reference 61 a and thelast guide roll thereof with the reference 61 b, and there is a doctor64 in connection with the guide roll 61 b.

The embodiment shown in FIG. 2 corresponds to that of FIG. 1 except thatboth the re-press nip PP and the single-felted press nip proper N₁,provided with an upper felt 30 are formed against the same transfer belt40B. In FIG. 2, the horizontal run of the lower transfer belt 40Bextends from its guide roll 41 a situated before the pre-press zone PPthrough the extended-nip press N₁ to its last guide roll 41 b, in whoseconnection there is a doctor 44.

The embodiment shown in FIG. 3 corresponds to that of FIG. 1 except thatthe pre-press nip PP is followed by a double-felted 30,60 first pressnip proper N₁ of the press section and it is followed by a second pressnip N₂ provided with one dewatering felt 50 and with a transfer belt 80.In FIG. 3, the lower felt passing through the first extended-nip zone N₁extends from its first guide roll 61 a to its last guide roll 61 b, andthe web W is separated from the upper felt 30 on a suction zone 64 of atransfer suction roll 64 and transferred on the lower felt 60 onto anupper felt 50 of the second extended nip N₂ on a suction zone 51 a of asuction transfer roll 51 situated inside the loop of the upper felt 50,said suction zone taking the web W into the second extended nip N₂. Thelower fabric of this extended nip N₂ is a transfer belt 80, whosehorizontal run extends from its first guide roll 81 a to its last guideroll 81 b.

In the figure, dashed lines denote with the reference 10A an alternativerun of a special transfer wire from a guide roll 13A to the transfersuction roll 15. In that case, there is no upper wet wire 10 or, whenthe twin-wire former 100 is used, the run of an upper wire 10B is likethe one indicated with the reference 10B and with guide rolls 13B.However, it may be emphasized in this connection that the bestembodiment of the invention is the one which expressly uses a twin-wireformer and an upper wet wire 10 and a lower wet wire 20 as well as apre-press zone PP in the manner shown in FIGS. 1-3 or in a correspondingway.

The claims are presented in the following and the various details of theinvention may vary within the inventive idea defined in said claims anddiffer from the disclosure given above by way of example only.

What is claimed is:
 1. A method for transferring a paper web (W) from aformer paper section (100) of a paper machine to a press section (110)thereof, said former section (100) having a lower wet wire loop (20) andan upper wet wire loop (10), said lower wire and said upper wet wiredefining a twin-wire forming zone, said press section having at leastone dewatering press nip (N₁; N₁,N₂), and a pre-press zone (PP)structured and arranged between said former section (100) and said presssection (110) for removing water from said web (W) passing therethroughas a closed draw from said former section (100) to said press section(110), comprising the steps of: providing at least a first pressuredifference device (15, 16) interiorly of said loop of said upper wetwire and at least a second pressure difference device (26) interiorly ofsaid loop of said lower wet wire for applying a pressure to said paperweb (W); and applying a pressure difference to said paper web (W)through said lower wet wire (20) and said -upper wet wire (10) after theformation of said paper web (W), such that, a higher pressure is appliedon one of: a side of said upper wet wire (10) in order for said paperweb (W) to follow said lower wet wire (20) during a threading operationor during an operational malfunction, and a side of said lower wet wire(20) in order for said paper web (W) to follow along said upper wet wire(10) during normal operating conditions.
 2. The method according toclaim 1, wherein when said web (W) is desired to be passed into a wirepit, comprising the step of: ensuring the run of the web (W) remains onthe face of the lower wire web (20) by means of vacuums created throughsuction devices (26) structured and arranged inside a loop of said lowerwet wire (20), and simultaneously preventing the run of the web (W)along said upper wet wire (10) by one of closing a vacuum zone (15 a) ofone of said pressure difference devices (15) and introducing a positivepressure on to said upper wet wire (10).
 3. The method according toclaim 1, further comprising the steps of: connecting a vacuum to asuction zone (15 a) of a transfer suction device (15) structured andarranged inside a loop of one of said upper wet wire (10) when said web(W) is transferred into a pre-press zone (PP) and simultaneously intoone of a press nip (N₁) and a plurality of press nips (N₁,N₂); andsimultaneously, when needed, lowering the vacuum level in a suctiondevice (26) structured and arranged in said lower wet wire (20) suchthat said web (W) follows said upper wet wire (10) into said pre-presszone (PP).
 4. The method according to claim 1, further comprising thesteps of: separating said paper web (W) after said pre-press zone (PP)form said upper wet wire (10); and passing said paper web (W), as aclosed draw, on an upper face of a substantially non-water-receivingtransfer belt (40A,40B) onto a lower face of an upper fabric (30) of afollowing press nip (N₁), in a machine running direction, through saidpress nip (N₁) onto a drying wire (90) of a dryer section (120)structured and arranged after said press section (110) in a machinerunning direction.
 5. The method according to claim 4, wherein saidfollowing press nip (N₁) is one of a suction roll transfer (30,31 a) anda closed draw on said upper face of said transfer belt (40B).
 6. Themethod according to claim 1, further comprising the steps of: applyingsaid pressure difference to said web (W) through said upper wet wire(10) and said lower wet wire (20) when said web (WO has a dry solidslevel in the range of about 10% to about 15%; and raising said drysolids level of said web (W) in said pre-press zone (PP) to a range ofabout 18% to about 35%.
 7. A former-press section of a paper machinecomprising: a former section having a lower wet wire arranged in a loopand an upper wet wire arranged in a loop, said lower wet wire and saidupper wet wire defining a twin-wire forming zone; a press section havingat least one detwatering nip; a pre-press zone arranged between saidformer section and said press section which removes water from a webpassed as a closed draw from the former section to the press section;wherein said upper wet wire is structured and arranged to pass throughsaid pre-press zone and said web is on a lower face of said upper wire;at least a first transfer device arranged interiorly of said loop ofsaid upper wet wire and at least a second transfer device arrangedinteriorly of said loop of said lower wet wire, said transfer devicesbeing structured and arranged to generate a pressure difference toensure that during normal operation of said paper machine said webseparates from said lower wet wire and follows said upper wet wire on alower face thereof into said pre-press zone and wherein during one ofthreading and operational malfunction conditions of said paper machinesaid transfer devices are structured and arranged to insure that saidweb is separated from said upper wet wire and falls down into one of awire pit, pulper and equivalent situated underneath said upper wet wire.8. The former-press section according to claim 7, further comprising asubstantially non-water-receiving transfer belt arranged to run throughsaid pre-press zone said transfer belt being structured and arranged tocause said web to separate from said upper wet wire and adhere to anupper face of said transfer belt in said pre-press zone.
 9. Theformer-press section of claim 8, further comprising: a water receivingupper press felt arranged after the pre-press zone in a runningdirection of said paper machine; a suction roll structured and arrangedto transfer said web from said substantially non-water-receivingtransfer belt to a lower face of said water receiving upper press felt;a first dewatering press nip arranged after said suction roll in arunning direction of said paper machine through which said web on saidupper press felt passes; a lower press felt structured and arranged sothat lower press felt and said upper press felt define a closed drawafter said first dewatering press nip web, and wherein said lower pressfelt is structure arranged to carry said web on an upper face thereofafter said first dewatering nip and wherein said lower press felt isstructured and arranged to pass said web onto a drying wire of a dryersection of said paper machine.
 10. The former-press section according toclaim 8, further comprising: a nip arranged after said pre-press zone;wherein said substantially non-water-receiving transfer belt isstructured and arranged to pass through said nip.
 11. The former-presssection according to claim 7, further comprising a suction transferdevice arranged inside said loop of said upper wire and wherein saidsuction transfer device is structured and arranged to generate a vacuumeffect to ensure that said web follows said upper wet wire into saidpre-press zone.
 12. The former-press section of claim 11, furthercomprising a suction box arranged substantially immediately after saidsuction transfer device in a running direction of said paper machine andwherein said suction box is arranged within said loop of said lower wireand is structured and arranged to ensure that said web follows saidlower wire during said threading and operational malfunction conditions.13. The former-press section of claim 7, further comprising at least onesuction box arranged inside the loop of the upper wet wire.